JP2006062291A - Inkjet head, control method therefor, and inkjet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet head which can form a high-quality image at a high speed by rapidly and surely supplying coloring material particles to an ejection port, and a control method for the inkjet head. <P>SOLUTION: In this inkjet head 10, an ejection-port substrate 16, wherein an ejection port 28 is formed, is provided with an ejection electrode 18 which is composed of an upstream-side electrode 18a, a downstream-side electrode 18b and intermediate electrodes 18c and 18d. A control part 33, which can control a voltage applied to the ejection electrode 18, controls each of voltages which are applied to the respective electrodes, constituting the ejection electrode 18, so that an asymmetrical electric field can be formed in the ejection port 28 in the nonejection of ink. This enables the coloring material particles to be rapidly and surely flocculated in the ejection port 28, and enables the high-quality image to be formed on the recording medium at the high speed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink jet head, a control method therefor, and a recording apparatus using the ink jet head, and more particularly, an ink jet head that discharges ink containing charged fine particles using electrostatic force, a control method therefor, and a recording apparatus. About.

  There is known an electrostatic ink jet recording method in which ink is ejected toward a recording medium using an electrostatic force. In the electrostatic ink jet recording system, ink containing charged fine particle components is used, and a driving voltage is applied to the ejection electrodes arranged around the nozzles for ejecting the ink so that an electrostatic force acts on the ink of the nozzles. Ink droplets are ejected from the nozzles toward the recording medium. By controlling the drive voltage applied to the ejection electrodes according to the image data, an image corresponding to the image data can be recorded on the recording medium.

  An electrostatic ink jet head according to the electrostatic ink jet recording system has a relatively simple structure, and thus has a feature that it is easy to make a multi-channel in which a plurality of ejection portions (channels) are arranged. Further, since minute droplets can be formed, an image can be formed on a recording medium with high resolution.

The present inventor disclosed in Japanese Patent Application Laid-Open No. 2004-228688 an inkjet image recording apparatus capable of recording a high-quality image by fixing colored particles on a recording medium and recording images on both sides of the recording medium. . In this Patent Document 1, an insulating ink containing a coloring material and dispersed with charged fine particles (coloring material particles) is used as the ink. Such insulating ink causes dot bleeding on a recording medium. Since it does not occur easily, there is an advantage that there is almost no need to select a recording medium according to the ink.
JP 2004-181644 A

In order to draw an image with high image quality and high speed on a recording medium using an electrostatic ink jet head, it is necessary to quickly supply a sufficient amount of charged color material particles to the ejection unit. As a method for rapidly supplying the color material particles to the discharge unit, for example, a method of using a liquid flow or moving the color material particles to the discharge port by electrophoresis can be considered.
However, these methods alone are not sufficient to supply a sufficient amount of colorant particles to the ejection portion quickly, clogging of the ejection port of the inkjet head, and the division of dots formed on the recording medium There is a risk of causing problems such as.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to supply color material particles to a discharge port quickly and surely and to draw at high speed, and to produce an image with high image quality. An inkjet head that can be formed, a control method thereof, and an inkjet recording apparatus.

  In order to solve the above-described problem, a first aspect of the present invention is an electrostatic inkjet head that records an image on a recording medium by ejecting ink containing charged fine particles using electrostatic force, An ejection port substrate on which ejection ports for ejecting the ink are formed; and an ink flow path for supplying the ink to the ejection ports, provided on the opposite side of the ejection port substrate to the ink ejection side. A plurality of electrodes, the discharge electrodes formed on the discharge port substrate so as to surround the discharge ports, and applied with a voltage for discharging the ink from the discharge ports; and the ink An electrostatic ink jet head having a control unit for controlling voltages applied to the plurality of electrodes constituting the discharge electrode so that an asymmetric electric field is formed at the discharge port during non-discharge To provide.

  In the inkjet head according to the aspect of the invention, the control unit may apply a voltage to be applied to each of the plurality of electrodes constituting the ejection electrode so that a symmetrical electric field is formed with respect to the center of the ejection port when the ink is ejected. It is preferable to control.

Moreover, it is preferable that the discharge port is formed in a long hole shape that is long in the ink flow direction of the ink flow path.
The plurality of electrodes constituting the discharge electrode are preferably arranged so as to be asymmetric with respect to a plane perpendicular to the ink flow direction of the ink flow path and including the center of the discharge port. .

  In addition, the discharge electrode is disposed upstream of the discharge port in the ink flow direction of the ink flow path and downstream of the upstream electrode, and is substantially C-shaped or It is preferable that it is comprised from the downstream electrode which has a substantially U-shaped shape. Alternatively, the ejection electrode is disposed on the downstream side of the ejection port in the ink flow direction of the ink flow path and on the upstream side of the downstream electrode, and is substantially C-shaped or It is preferable that it is comprised from the upstream electrode which has a substantially U-shaped shape.

  The plurality of electrodes constituting the ejection electrode are preferably arranged so as to be symmetric with respect to a plane perpendicular to the ink flow direction of the ink flow path and including the center of the ejection port. In addition, the ejection electrode includes an upstream electrode disposed upstream of the ejection port in the ink flow direction of the ink flow path, a downstream electrode disposed downstream of the ejection port, and It is preferable to be composed of a pair of intermediate electrodes located between the upstream electrode and the downstream electrode and arranged so as to sandwich the discharge port.

  In the ink jet head of the present invention, a plurality of the discharge ports are formed, and at least one of the plurality of electrodes constituting the discharge electrode disposed in each discharge port is electrically common to each other. It is preferable.

  In order to solve the above problems, a second aspect of the present invention provides an ink jet recording apparatus including the ink jet head according to the first aspect of the present invention.

  In order to solve the above problems, a third aspect of the present invention is a method for controlling an electrostatic ink jet head that records an image on a recording medium by ejecting ink containing charged fine particles using electrostatic force. The electrostatic inkjet head is provided on a side of the discharge port substrate opposite to the side on which the ink is discharged of the discharge port substrate on which the discharge port for discharging the ink is formed. An ink flow path for supplying the ink and a plurality of electrodes are formed on the discharge port substrate so as to surround the discharge ports, and for discharging the ink from the discharge ports. The plurality of electrodes constituting the discharge electrode so that an asymmetric electric field is formed with respect to a central axis of the discharge port when the ink is not discharged. Respectively To provide a control method for controlling a voltage to be pressurized.

  In the control method of the present invention, the voltage applied to each of the plurality of electrodes constituting the ejection electrode is controlled so that an electric field symmetric with respect to the central axis of the ejection port is formed when the ink is ejected. It is preferable to apply a voltage having the same voltage value to all the electrodes constituting the discharge electrode when the ink is discharged.

  In addition, one of the plurality of electrodes constituting the ejection electrode is an upstream electrode disposed on the upstream side in the ink flow direction of the ink flow path, and the non-ejection electrode is charged with the charging electrode. It is preferable to apply a voltage having a polarity opposite to that of the fine particles, and one of the plurality of electrodes constituting the ejection electrode is a downstream electrode disposed on the downstream side in the ink flow direction of the ink flow path, It is preferable to apply a voltage having the same polarity as that of the charged fine particles to the downstream electrode during non-ejection.

  In addition, it is preferable that the voltage applied to the plurality of electrodes is controlled so that the application time of the voltage applied to the plurality of electrodes constituting the ejection electrode is different when the ink is ejected.

In the ink jet head of the present invention, the discharge electrode to which the voltage for discharging ink from the discharge port is applied is composed of a plurality of electrodes, and when the ink is not discharged, the asymmetrical material is likely to collect the color material particles at the discharge port. The voltage applied to the plurality of electrodes is controlled by the control unit so that an electric field is formed. As a result, the color material particles in the ink can be aggregated at the ejection port by an asymmetric electric field, and an image can be drawn on the recording medium at a high speed and an image can be formed with high image quality.
In addition, since the ink jet recording apparatus of the present invention includes the ink jet head of the present invention, an image can be formed on a recording medium at high speed and with high image quality.
In addition, according to the control method of the ink jet head of the present invention, since the color material particles can be quickly and reliably supplied to the ejection port, it is possible to draw an image on a recording medium at a high speed and to achieve high image quality. An image can be formed.

Hereinafter, an ink jet head, a control method thereof, and an ink jet recording apparatus according to the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
FIG. 1 (A) schematically shows a cross-section of the schematic configuration of the ink jet head according to the present invention, and FIG. 1 (B) shows a BB line arrow view of FIG. 1 (A). As shown in FIG. 1A, the inkjet head 10 includes a head substrate 12, an ink guide 14, and an ejection port substrate 16 on which ejection ports 28 are formed. On the discharge port substrate 16, discharge electrodes 18 are arranged so as to surround the discharge port 28. A counter electrode 24 that supports the recording medium P and a charging unit 26 of the recording medium P are disposed at a position facing the ink discharge side surface (upper surface in the drawing) of the inkjet head 10.
In addition, the head substrate 12 and the discharge port substrate 16 are arranged at a predetermined interval while facing each other. An ink flow path 30 that supplies ink to each ejection port 28 is formed by a space formed between the head substrate 12 and the ejection port substrate 16.

  The inkjet head 10 has a multi-channel structure in which a plurality of ejection ports 28 (nozzles) are two-dimensionally arranged in order to perform higher density image recording at high speed. FIG. 2 schematically shows a state in which a plurality of discharge ports 28 are two-dimensionally arranged on the discharge port substrate 16 of the inkjet head 10. In FIGS. 1A and 1B, only one of the plurality of discharge ports is shown for easy understanding of the configuration of the inkjet head.

  In the inkjet head 10 of the present invention, the number of ejection ports 28, the physical arrangement position thereof, and the like can be freely selected. For example, not only a multi-channel structure as shown in FIG. 2 but also a single discharge port may be provided. Further, a so-called (full) line head having a row of ejection openings corresponding to the entire area of the recording medium P may be used, or a so-called serial head (shuttle type) scanned in a direction orthogonal to the direction of the nozzle row. Good. The ink jet head of the present invention can be used for both monochrome and color recording apparatuses.

FIG. 2 shows an arrangement of a part of the multi-channel structure (3 rows and 3 columns), and in a preferred embodiment, in the ink flow direction, the outlets 28 on the downstream side are arranged on the upstream side. The nozzles are arranged so as to be shifted by a predetermined pitch in the direction perpendicular to the ink flow with respect to the ejection ports. In this way, by disposing the discharge ports in the downstream row in a direction perpendicular to the ink flow direction with respect to the discharge ports in the upstream row, it is possible to satisfactorily supply ink to the discharge ports. In the inkjet head of the present invention, n rows and m columns (n and m are positive) are arranged such that the discharge ports in the downstream column are shifted in the direction perpendicular to the ink flow direction with respect to the discharge ports in the upstream column. May be configured such that each of the discharge ports is perpendicular to the ink flow with respect to the discharge ports located on the upstream side. They may be continuously shifted in the direction (downward or upward in FIG. 2). The number, pitch, repetition period, and the like of the discharge ports can be appropriately set according to the resolution and the feed pitch.
In addition, in FIG. 2, as a preferred mode, in the ink flow direction, the discharge ports in the downstream row are shifted from the discharge ports in the upstream row in the direction perpendicular to the ink flow, but the present invention is not limited to this. Instead, the downstream outlet and the upstream outlet may be arranged on the same straight line in the ink flow direction. In this case, it is preferable to dispose each ejection port in each row in the ink flow direction with respect to each ejection port in a row adjacent to the row in a direction perpendicular to the ink flow.

  In such an ink jet head 10, an ink Q is used, which includes a coloring material such as a pigment and is dispersed in an insulating liquid (carrier liquid) with charged fine particles (hereinafter referred to as coloring material particles). . Then, a driving voltage is applied to the ejection electrode 18 provided on the ejection port substrate 16 to generate an electric field at the ejection port 28, and the ink in the ejection port 28 is ejected by electrostatic force. Further, by turning on / off the drive voltage applied to the ejection electrode 18 according to the image data (ejection on / off), the ink droplets are ejected from the ejection port 28 according to the image data, and the recording medium P Record the image on top.

  Hereinafter, the structure of the inkjet head 10 of the present invention shown in FIGS. 1A and 1B will be described in more detail.

  As shown in FIG. 1A, the discharge port substrate 16 of the inkjet head 10 includes an insulating substrate 32, a guard electrode 20, a discharge electrode 18, and an insulating layer 34. A guard electrode 20 and an insulating layer 34 are sequentially stacked on the upper surface of the insulating substrate 32 in the drawing (the surface opposite to the side facing the head substrate 12). A discharge electrode 18 to which a voltage for discharging ink is applied is formed on the lower surface of the insulating substrate 32 in the drawing (the surface facing the head substrate 12).

  Further, the discharge port substrate 16 is formed with a discharge port 28 for discharging the ink droplet R penetrating the insulating substrate 32. As shown in FIG. 1B, the ejection port 28 is a rectangular opening (slit) elongated in the ink flow direction, and the four corners of the rectangular ejection port 28 are rounded. Here, the ejection port 28 is formed in a rectangular shape. However, the present invention is not limited to this, and as long as ink can be ejected from the ejection port 28, a circular shape, a substantially circular shape, an elliptical shape, a square shape, a rhombus shape, a parallelogram shape, and the like. Any shape can be used. The shape of the ejection port 28 is preferably an elongated shape in the ink flow direction. For example, a rectangular shape having a long side in the ink flow direction, or an ellipse or a rhombus having a long axis in the ink flow direction can be used. Alternatively, the upstream side of the ink flow may be an upper base, the downstream side may be a lower bottom, and the height in the ink flow direction may be longer than the lower base. In this case, the upstream side may be lengthened or the downstream side may be lengthened. Moreover, you may make it the shape which made the short side of both rectangles the semicircle. Alternatively, a shape in which a circle having a diameter larger than the short side of the rectangle is connected to both short sides of the rectangle having the long side in the ink flow direction. Thus, by making the ejection port 28 elongated in the ink flow direction, it is possible to improve the ink supply property to the ejection port 28 and to prevent clogging. Further, the discharge port 28 may have a symmetric shape or an asymmetric shape on the upstream side and the downstream side with respect to the center thereof. For example, the discharge port may be formed by semicircularly forming at least one end on the upstream side and the downstream side of the rectangular discharge port as shown in FIG.

  The ink guide 14 of the inkjet head 10 is made of a ceramic flat plate having a predetermined thickness, and is disposed on the head substrate 12 corresponding to each ejection port 28 (ejection unit). The ink guide 14 is formed wide according to the length of the rectangular discharge port 28 in the long side direction. As described above, the ink guide 14 passes through the ejection port 28, and the tip end portion 14 a projects upward from the surface of the ejection port substrate 16 on the recording medium P side (the surface of the insulating layer 34).

The leading end portion 14a of the ink guide 14 is formed into a substantially triangular shape (or trapezoid) that gradually becomes thinner toward the counter electrode 24 side. The ink guide 14 is disposed such that the inclined surface of the tip portion 14a intersects the ink flow direction. As a result, the ink flowing into the ejection port 28 reaches the apex of the distal end portion 14 a along the inclined surface of the distal end portion 14 a of the ink guide 14, so that an ink meniscus is stably formed at the ejection port 28.
The shape of the ink guide 14 is not particularly limited as long as the charged fine particle component in the ink Q can be concentrated to the tip portion 14a through the discharge port 28 of the discharge port substrate 16. For example, the shape of the ink guide 14 is not limited. The shape does not have to be thinned toward the counter electrode, and can be changed as appropriate. For example, a cutout serving as an ink guide groove that collects the ink Q in the front end portion 14a may be formed in the center portion of the ink guide 14 in the vertical direction in the drawing by capillary action. In FIG. 1B, a plate-like shape that is long in the ink flow direction is used in accordance with the shape of the ejection port. However, the shape is not limited to this, and a prism may be used.
Further, it is preferable that a metal is deposited on the most advanced portion of the ink guide 14. By depositing metal on the leading edge of the ink guide 14, the dielectric constant of the tip portion 14a of the ink guide 14 is substantially increased. Thereby, it becomes easy to generate a strong electric field, and the discharge property of ink can be improved.

  As shown in FIG. 1B, a discharge electrode 18 divided into four independent electrodes is formed on the lower surface (the surface facing the head substrate) of the insulating substrate. That is, as shown in FIG. 1B, the ejection electrode 18 includes an electrode (upstream electrode) 18a disposed upstream of the ejection port in the ink flow direction and an electrode (downstream electrode) disposed downstream. ) 18b and a pair of electrodes (intermediate electrodes) 18c and 18d along the long side of the discharge port 28. The upstream electrode 18a, the downstream electrode 18b, and the intermediate electrodes 18c and 18d are arranged along the short side and the long side of the rectangular discharge port 28 so as to surround the periphery of the rectangular discharge port 28. The intermediate electrodes 18c and 18d are located between the upstream electrode 18a and the downstream electrode 18b, and are disposed so as to sandwich the discharge port 28 therebetween. Further, the intermediate electrode 18c and the intermediate electrode 18d are electrically connected by a wiring (not shown). In FIG. 1B, each electrode constituting the discharge electrode 18 is formed in a rectangular shape, but is not limited thereto, and can be changed to various shapes depending on the shape of the discharge port 28.

As described above, since the inkjet head 10 has a multi-channel structure in which the discharge ports 28 are two-dimensionally arranged, the discharge electrode 18 corresponds to each discharge port 28 as schematically shown in FIG. They are arranged two-dimensionally.
Further, all of the ejection electrodes 18 (upstream electrode 18a, downstream electrode 18b, intermediate electrodes 18c and 18d) are exposed to the ink flow path 30 and are in contact with the ink Q flowing through the ink flow path 30. Thereby, the discharge property of ink droplets can be greatly improved. This point will be described later together with the action of discharge. However, the electrodes constituting the ejection electrode 18 are not necessarily exposed to the ink flow path 30 and are not in contact with the ink. That is, each electrode constituting the discharge electrode 18 may be formed inside the discharge port substrate 16, or the exposed surface of each electrode may be covered with a thin insulating layer or the like. Further, of the electrodes constituting the ejection electrode 18, any electrode may be in contact with the ink in the ink flow path 30, and the other electrode may be covered with an insulating layer so as not to contact the ink.

  Each electrode constituting the discharge electrode 18 is connected to the control unit 33 as shown in FIG. The controller 33 can control the voltage applied to each electrode during ink ejection and during non-ejection. A method for controlling the voltage by the control unit 33 will be described in detail later.

In the ink jet head shown in FIG. 1B, the discharge electrode 18 has a structure in which four electrodes are arranged along the four sides of the rectangular discharge port 28, but the shape of the discharge electrode 18 is limited to this. For example, as shown in FIG. 3, an electrode (upstream electrode) 18a is arranged along the upstream side of the discharge port 28, and three downstream sides of the upstream electrode 18a, that is, the discharge side. Even if the U-shaped electrode (downstream electrode) 18b is formed along three sides other than the one side on the upstream side of the outlet 28, the discharge electrode 18 is configured by the upstream electrode 18a and the downstream electrode 18b. Good.
On the other hand, as shown in FIG. 4, an electrode (downstream electrode) is arranged along one side on the downstream side of the discharge port 28, and a U-shape is formed along three sides on the upstream side of the discharge port. The discharge electrode 18 may be configured by arranging a shaped electrode (upstream electrode).
Thus, in the ink jet head of the present invention, the discharge electrode 18 disposed so as to surround the discharge port 28 is configured to be divided at least into the upstream side and the downstream side in the ink flow direction.
In the discharge electrode shown in FIGS. 3 and 4, one of the upstream electrode 18a and the downstream electrode 18b has a U-shape, but the three sides of the discharge port 28 (long side and upstream or downstream side). Any shape can be used as long as the shape surrounds the short side. For example, the discharge port may be formed in an elliptical shape having a major axis in the long side direction of the discharge port, with a part of the upstream side or the downstream side notched.

The guard electrode 20 is formed on the surface of the insulating substrate 32, and the surface of the guard electrode 20 is covered with an insulating layer 34. FIG. 5 schematically shows a planar structure of the guard electrode 20. FIG. 5 is a view taken along the line VV in FIG. 1A, and schematically shows a planar structure of the guard electrode 20 in the case of an inkjet head having a multichannel structure. As shown in FIG. 5, the guard electrode 20 is a sheet-like electrode common to each discharge electrode such as a metal plate, and the discharge electrode 18 formed around each discharge port 28 arranged two-dimensionally. Has an opening 36 at a position corresponding to. The opening 36 is formed in a rectangular shape similar to the shape of the discharge port 28. The length and width of the opening 36 of the guard electrode 20 are formed larger than the length and width of the discharge port.
The guard electrode 20 can shield electric lines of force between the adjacent ejection electrodes 18 to suppress electric field interference, and a predetermined voltage is applied to the guard electrode 20 (including 0 [V] due to grounding). . In the illustrated example, the guard electrode 20 is grounded to 0 [V].

As a preferred embodiment, the guard electrode 20 is formed in a layer different from the ejection electrode 18 as shown in FIG. 1A, and the entire surface is covered with an insulating layer 34.
By having such a guard electrode 20, it is possible to suitably prevent electric field interference between the adjacent ejection electrodes 18, and the color material particles of the ink Q form a film between the ejection electrode 18 and the guard electrode 20 and discharge. Can also be prevented.

Here, the guard electrode 20 secures the electric lines of force that act on the corresponding discharge ports 28 (hereinafter referred to as “own channels” for convenience) among the electric lines of force generated from the discharge electrodes 18. It is necessary to provide the electric lines of force of the discharge electrode 18 provided in the discharge port 28 (also referred to as “other channels”) and the electric lines of force to the other channels.
In the absence of the guard electrode 20, the electric lines of force generated from the discharge port side end portions of the electrodes constituting the discharge electrode 18 (hereinafter referred to as the inner edge portion of the discharge electrode) during discharge of ink droplets are It converges on the inner side, that is, in the region surrounded by the inner edge of each electrode constituting the ejection electrode 18 and acts on its own channel to generate an electric field necessary for ejection of ink droplets. On the other hand, the lines of electric force generated from the end of each electrode constituting the discharge electrode 18 opposite to the discharge port side (hereinafter referred to as the outer edge of the discharge electrode) diverge further outward than the outer edge of the discharge electrode 18. Affects other channels and causes electric field interference.

In consideration of the above points, the width and length of the rectangular opening 36 of the guard electrode 20 are such that the discharge of the self-channel is not observed when viewed from the plane of the substrate so as not to shield the lines of electric force to the self-channel. It is preferable that the distance between the upstream electrode 18a and the downstream electrode 18b constituting the electrode 18 is larger than the distance between the intermediate electrodes 18c and 18d. In other words, the end of the guard electrode 20 on the discharge port 28 side is preferably separated (retreated) from the discharge port 28 rather than the inner edge of the discharge electrode 18 of the own channel.
Further, in order to efficiently shield the lines of electric force to other channels, the length and width of the rectangular opening 36 of the guard electrode 20 are set so that the discharge electrode 18 of the own channel when viewed in the substrate plane. Is preferably smaller than the distance between the outer edge portions of the upstream electrode 18a and the downstream electrode 18b and the distance between the outer edge portions of the intermediate electrodes 18c and 18d. That is, it is preferable that the inner edge portion of the guard electrode 20 is closer (advanced) to the discharge port 28 than the outer edge portion of each electrode constituting the discharge electrode 18 of the own channel. According to the study of the present inventor, this proximity amount is preferably 5 μm or more, particularly preferably 10 μm or more.
By having the above-described configuration, the ejection stability from the ejection port 28 is sufficiently ensured, and variations in the ink landing position due to electric field interference between adjacent channels are suitably suppressed, and the stability can be increased. It is possible to perform image recording with high image quality.

  The opening 36 of the guard electrode 20 is substantially similar to the shape formed by the inner edge or the outer edge of the ejection electrode 18, and the inner edge of the guard electrode 20 is more ejected than the inner edge of the ejection electrode 18 of its own channel. The guard electrode 20 may be provided so as to be separated from (retracted from) 28 and closer to (advance) the discharge port 28 than the outer edge of the discharge electrode (that is, the opening 36 of the guard electrode 20 may be formed). Good).

In the above example, the guard electrode 20 is a sheet-like electrode. However, the present invention is not limited to this, and may be provided so as to shield the electric lines of force of other channels between the discharge ports. Any shape or structure may be used. For example, the guard electrode 20 may be provided in a mesh shape between the discharge ports. In addition, in a plurality of discharge ports arranged in a matrix, for example, when the intervals between adjacent discharge ports in the row direction and the column direction are different, between the discharge ports sufficiently separated so as not to cause electric field interference. May not be provided with a guard electrode, and a card electrode may be provided only between adjacent outlets.
Even in such a case, the inner edge portion of the guard electrode 20 is further away from the discharge port 28 than the inner edge portion of the discharge electrode 18 with respect to the discharge electrode 18 of the self-channel, and the discharge port 28 is separated from the outer edge portion of the discharge electrode 18. The guard electrode 20 may be formed so as to be close to the electrode.
Here, the shape of the opening 36 of the guard electrode 20 is substantially the same as the shape of the discharge port 28, but the shape is not limited to this, and the lines of electric force between the adjacent discharge electrodes 18 are shielded. As long as the electric field interference can be prevented, it can be formed into an arbitrary shape. For example, the shape may be a circle, an ellipse, a square, a rhombus, or the like.

As shown in FIG. 1A, the counter electrode 24 is disposed so as to face the ejection surface of the ink droplet R of the inkjet head 10.
The counter electrode 24 is disposed at a position facing the front end portion 14a of the ink guide 14, and is disposed on the grounded electrode substrate 24a and the lower surface of the electrode substrate 24a in the drawing, that is, the surface on the inkjet head 10 side. The insulating sheet 24b is used.
The recording medium P is held on the lower surface of the counter electrode 24 in the drawing, that is, the surface of the insulating sheet 24b by, for example, electrostatic adsorption, and the counter electrode 24 (insulating sheet 24b) is used as a platen of the recording medium P. Function.

At least during recording, the recording medium P held on the insulating sheet 24b of the counter electrode 24 is charged by the charging unit 26 to a predetermined negative high voltage having a polarity opposite to the drive voltage applied to the ejection electrode 18.
As a result, the recording medium P is negatively charged and biased to a negative high voltage, acts as a substantial counter electrode with respect to the ejection voltage 18, and is electrostatically adsorbed to the insulating sheet 24 b of the counter electrode 24.

  The charging unit 26 includes a scorotron charger 26a for charging the recording medium P to a negative high voltage, and a bias voltage source 26b for supplying a negative high voltage to the scorotron charger 26a. The charging means of the charging unit 26 used in the present invention is not limited to the scorotron charger 26a, and various discharging means such as a corotron charger, a solid charger, and a discharge needle can be used.

In the illustrated example, the counter electrode 24 includes an electrode substrate 24a and an insulating sheet 24b, and the recording medium P is charged to a negative high voltage by the charging unit 26, whereby a bias voltage is applied to the counter electrode. However, the present invention is not limited to this, and the counter electrode 24 is constituted only by the electrode substrate 24a, and the counter electrode 24 (electrode substrate 24a itself) is formed. May be connected to a negative high voltage bias voltage source so as to be constantly biased to a negative high voltage so that the recording medium P is electrostatically attracted to the surface of the counter electrode 24.
Further, the electrostatic adsorption of the recording medium P to the counter electrode 24 and the charging of the recording medium P to a negative high voltage or the application of a negative bias high voltage to the counter electrode 24 are separate negative high voltage sources. The holding of the recording medium P by the counter electrode 24 is not limited to the electrostatic adsorption of the recording medium P, and other holding methods and holding means may be used.

  The structure of the inkjet head of the present invention has been described in detail above. Next, a method for controlling the voltage applied to each electrode constituting the ejection electrode 18 of the inkjet head will be described.

First, as an example, a method for controlling the discharge electrode 18 that is divided into four as shown in FIG. 1B will be described taking an example in which the color material particles are positively charged. Control of the voltage of the ejection electrode 18 as described below is performed by the control unit 33.
In the case of the ejection electrode having the structure shown in FIG. 1B, a voltage (negative voltage) having a polarity opposite to that of the color material particles is applied to the upstream electrode 18a during non-ejection. When a negative voltage is applied to the upstream electrode 18a in this way, the color material particles contained in the ink flowing through the ink flow path 30 are attracted to the upstream electrode 18a by the electric field generated from the upstream electrode 18a. It flows toward the discharge port 28 where the upstream electrode 18a is disposed.
Further, a voltage (positive voltage) having the same polarity as that of the color material particles is applied to the downstream electrode 18b at the time of non-ejection. When such a positive voltage is applied to the downstream electrode 18b, the colorant particles contained in the ink present at the ejection port 28 are pressed against the ejection port 28 by the electric field generated from the downstream electrode 18b. .
On the other hand, no voltage is applied to the intermediate electrodes 18c and 18d during non-ejection, and the voltage is 0 [V].

As described above, in the ink jet head shown in FIG. 1B, the colorant particles contained in the ink are discharged to the discharge port 28 by the upstream electrode 18a and the downstream electrode 18b constituting the discharge electrode 18 when not discharging. Aggregate.
On the other hand, during discharge, a voltage having the same polarity as that of the colorant particles is applied to each electrode constituting the discharge electrode 18, that is, the upstream electrode 18a, the downstream electrode 18b, and the intermediate electrodes 18c and 18d. As a result, an electric field for ejecting ink droplets is generated in the vicinity of the ejection port 28, and the ink droplets are ejected from the ejection port 28. In particular, at the time of non-ejection, since the color material particles are aggregated in the ejection port 28 as described above, ink droplets having a sufficient concentration are ejected from the ejection port 28. The ink droplet ejection action will be described in detail later.

  Here, the voltage applied to each electrode will be described using a timing chart. FIG. 6 shows an example of a timing chart of the voltage applied to each electrode. As shown in FIG. 6, at the time of non-ejection, a negative voltage of −50 [V] is applied to the upstream electrode 18a, a positive voltage of 0 [V] is applied to the intermediate electrodes 18c and 18d, and a positive voltage of +50 [V] is applied to the downstream electrode 18b. Is done. That is, during non-ejection, voltages having different voltage values are applied to the electrodes constituting the ejection electrode 18. For this reason, during non-ejection, the electric field near the ejection port 28 is asymmetric with respect to the center of the ejection port 28, that is, with respect to the ink guide 14. If the voltage applied to each electrode constituting the discharge electrode 18 is controlled according to the timing shown in FIG. 6, the color material particles are guided to the discharge port 28 by the electric field generated from the upstream electrode 18a, and the color material particles are The electric field from the downstream electrode 18b is held in the ejection port 28 against the ink flow. In this way, the color material particles in the ink flow path 30 are aggregated at the ejection port 28.

  Here, at the time of non-ejection, a voltage having the same polarity as that of the color material particles is applied to the downstream electrode 18b constituting the divided ejection electrode 18, and ink may be ejected by the electric field of the downstream electrode 18b. There is. However, since the electric field formed in the vicinity of the ejection port 28 is asymmetric during non-ejection, and the voltage value applied to the downstream electrode 18b during non-ejection is not a sufficient voltage value for ejecting ink. Ink is not ejected from the ejection port 28.

  On the other hand, during discharge, a positive voltage of +300 [V] is simultaneously applied to each electrode constituting the discharge electrode 18, that is, the upstream electrode 18a, the downstream electrode 18b, and the intermediate electrodes 18c and 18d. In the following description, the voltage applied to each electrode constituting the ejection electrode 18 in order to eject ink is also referred to as “driving voltage”. By simultaneously applying a positive voltage (drive voltage) having the same voltage value to the discharge electrode 18 surrounding the discharge port 28, an electrostatic field is generated in the vicinity of the discharge port 28. As a result, an electrostatic force acts on the ink in the ejection port 28 and ink droplets are ejected from the ejection port 28. As described above, since the same voltage is applied to all the electrodes constituting the ejection electrode 18, the electric field in the vicinity of the ejection port 28 becomes a preferable electric field that is symmetric with respect to the center of the ejection port 28, that is, the ink guide 14. . Therefore, by applying a predetermined voltage to each electrode constituting the ejection electrode 18 in accordance with the timing chart shown in FIG. 6, ink droplets can be ejected stably toward the recording medium. The voltage value applied to each electrode constituting the ejection electrode 18 at the time of ejection and non-ejection is an example, and depends on the shape of the ejection port 28, the shape of each electrode constituting the ejection electrode 18, the ink used, etc. Thus, the voltage value can be changed as appropriate.

  Thus, in the present invention, a symmetric electric field is formed in the vicinity of the discharge port 28 during discharge. The reason is that if an asymmetric electric field is formed in the vicinity of the ejection port 28 during ejection, the ejection position and ejection direction of the ink droplets may fluctuate, and the shape of the dots formed on the recording medium may deteriorate. Because there is. In the above example, by applying the same voltage to each electrode constituting the ejection electrode 18 during ejection, the electric field in the vicinity of the ejection port 28 is prevented from becoming asymmetric, and the ejection position of the ink droplets fluctuates. The dot shape formed on the recording medium is prevented from being deteriorated. However, if a symmetric electric field is formed in the vicinity of the ejection port 28 during ejection and ink droplets can be ejected stably without fluctuations in the ejection position and direction, the same voltage is applied to each electrode. For example, the voltage applied to the upstream electrode 18a and the downstream electrode 18b during discharge may be set to 0 [V], and a positive voltage may be applied only to the intermediate electrodes 18c and 18d. In this case, the voltage value applied to the intermediate electrodes 18c and 18d is set to a voltage value sufficient to cause ink to be ejected from the ejection port 28.

  FIG. 7 shows another timing chart of the drive voltage applied to the four-divided ejection electrode 18 shown in FIG. As shown in FIG. 7, before a pulse voltage for ejecting ink is applied, a negative voltage of −50 [V] is applied to the upstream electrode 18a for a predetermined application time. Further, a positive voltage of +50 [V] is applied to the downstream electrode 18b with the same application time as the negative voltage applied to the upstream electrode 18a. Accordingly, prior to ink ejection, a negative voltage having a polarity opposite to that of the color material particles is applied to the upstream electrode 18a, and the color material particles can be supplied to the ejection port 28 by the electric field generated from the upstream electrode 18a. . Further, at the same timing, a positive voltage having the same polarity as that of the color material particles is applied to the downstream electrode 18b, and an electric field generated from the downstream electrode 18b counteracts the ink flow in the ink flow path 30, thereby The material particles can be pressed against the discharge port 28. Then, when ink droplets are ejected from the ejection port 28 in accordance with the image data, as shown in FIG. 7, the upstream electrode 18a, the downstream electrode 18b, and the intermediate electrodes 18c and 18d are each 300 [ V] is applied. As a result, electrostatic force acts on the ink at the ejection port 28, and the ink is ejected from the ejection port 28. After ink ejection, each electrode is set to 0 [V].

  In the present invention, the voltage value applied to each electrode constituting the ejection electrode 18 at the time of ejection is not limited to the above voltage value, so that ink droplets can be reliably ejected from the ejection port 28 by electrostatic force. Any voltage value can be set to any voltage value.

  Here, at the time of ejection, the voltage applied to the upstream electrode 18a and the downstream electrode 18b is applied at a timing according to the image data, but may be applied at a constant timing regardless of the image data. That is, a voltage of +300 [V] may always be applied to the upstream electrode 18a and the downstream electrode 18b at a constant cycle. FIG. 8 shows an example of a timing chart according to such a control method. As shown in FIG. 8, even when ink droplets are not ejected, the same voltage value as that during ejection may be applied to the upstream electrode 18a and the downstream electrode 18b. In this case, the voltage applied to the ejection electrode 18 at the time of ejection is preferably adjusted so that ink is not ejected from the ejection port 28 only by applying the voltage to the upstream electrode 18a and the downstream electrode 18b. As described above, when the timing of the voltage applied to the upstream electrode 18a and the downstream electrode 18b is always constant, the upstream electrodes and the downstream electrodes of each channel can be electrically shared. . Further, since the voltages applied to the upstream electrode 18a and the downstream electrode 18b do not need to be controlled in accordance with the image data, the respective control units for controlling the upstream electrode 18a and the downstream electrode 18b. Can be configured in a simple manner.

  Next, an example of a method for applying a voltage to the ejection electrode 18 having the shape shown in FIG. 3 will be described. An example of a timing chart of the voltage applied to the ejection electrode 18 having the shape shown in FIG. 3 is shown in FIG. As shown in FIG. 9, a negative voltage of −50 [V] is applied to the upstream electrode 18a during non-ejection, and a voltage of +300 [V] is applied during ejection. On the other hand, the voltage is not applied to the downstream electrode 18b when it is not ejected, and is set to 0 [V]. At the time of ejection, the same voltage of +300 [V] as that of the upstream electrode 18a is applied. When a voltage is applied to the upstream electrode 18a and the downstream electrode 18b according to the timing chart of FIG. 9, a negative voltage having the same polarity as that of the colorant particles is applied to the upstream electrode 18a during non-ejection. The color material particles are promptly guided to the discharge port 28 by the electric field generated from the upstream electrode 18 a, and the color material particles are easily aggregated at the discharge port 28. At the time of ejection, a positive voltage of +300 [V] is applied to the upstream side electrode 18a and the downstream side electrode 18b in this state, so that the concentrated ink is ejected from the ejection port 28.

  Further, FIG. 10 shows an example of a timing chart of applied voltage different from FIG. As shown in FIG. 10, during non-ejection, no voltage is applied to the upstream electrode 18a, and the voltage is set to 0 [V]. In discharging, a positive voltage of 300 [V] is applied. Further, a positive voltage of +50 [V] is applied to the downstream electrode 18b during non-ejection, and a positive voltage of +300 [V] which is the same as that of the upstream electrode 18a is applied during ejection. As described above, when the voltage having the same polarity as that of the color material particles is applied to the downstream electrode 18b at the time of non-ejection, an electric field is generated from the downstream electrode 18b, and the color material of the ink flow path 30 is generated by the electric field. The particles are pressed against the ejection port 28 against the ink flow. Thereby, the density | concentration of the color material particle in the discharge outlet 28 is raised. At the time of ejection, a positive voltage of +300 [V] is applied to the upstream electrode 18a and the downstream electrode 18b in this state, and the concentrated ink is ejected from the ejection port 28.

  FIG. 11 shows still another timing chart of applied voltages. As shown in FIG. 11, at the time of non-ejection, a negative voltage of −50 [V] is applied to the upstream electrode 18a, and a positive voltage of +50 [V] is applied to the downstream electrode 18b. As a result, during non-ejection, the color material particles are promptly guided to the ejection port by the electric field generated from the upstream electrode 18a, and the color material particles at the ejection port 28 are against the flow by the electric field generated from the downstream electrode 18b. Thus, it is retained in the discharge port 28. In this way, the color material particles are aggregated at the discharge port 28 during non-discharge. At the time of ejection, as shown in FIG. 11, a positive voltage of +300 [V] is simultaneously applied to the upstream electrode 18a and the downstream electrode 18b. As a result, an electric field is generated from the upstream electrode 18a and the downstream electrode 18b surrounding the ejection port 28, and an electrostatic force acts on the ink at the ejection port by the electric field, and ink droplets are ejected from the ejection port.

  Also, in the case of the inkjet head having the discharge electrode having the shape shown in FIG. 4, the voltage is applied to the upstream electrode 18a and the downstream electrode 18b at the same timing as the timing charts shown in FIGS. Can be applied. That is, if a negative voltage of −50 [V] is applied to the upstream electrode 18a without applying a voltage to the downstream electrode 18b at the time of non-ejection according to the timing shown in FIG. 9, the voltage is generated from the upstream electrode 18a. Due to the electric field, the color material particles contained in the ink in the ink flow path 30 are quickly guided to the ejection port 28. Then, in the state where the color material particles are aggregated in the discharge port 28 in this way, at the time of discharge, a positive voltage of +300 [V] is applied to the upstream electrode 18a and the downstream electrode 18b to be concentrated from the discharge port. Ink droplets can be ejected.

  Further, according to the timing chart shown in FIG. 10, during non-ejection, a positive voltage of +50 [V] is applied to the downstream electrode 18b without applying a voltage to the upstream electrode 18a of the ejection electrode shown in FIG. For example, the color material particles in the ink flow path 30 are pressed against the ejection port 28 against the ink flow by the electric field generated from the downstream electrode 18b. In this state, during discharge, a positive voltage of +300 [V] is applied to the upstream electrode 18a and the downstream electrode 18b, so that the electric field generated from the upstream electrode 18a and the downstream electrode 18b concentrates from the discharge port 28. The discharged ink droplet is ejected.

  Further, in accordance with the timing chart shown in FIG. 11, at the time of non-ejection, a negative voltage of −50 [V] is applied to the upstream electrode 18a of the ejection electrode 18 shown in FIG. 4, and +50 [V] is applied to the downstream electrode 18b. When the positive voltage is applied, the color material particles are quickly guided to the discharge port by the electric field generated from the upstream electrode 18a, and the color material particles are pushed to the discharge port 28 by the electric field generated from the downstream electrode 18b. You can stay. In this state, during discharge, a positive voltage of +300 [V] is applied to the upstream electrode 18a and the downstream electrode 18b, and is concentrated from the discharge port 28 by the electric field generated from the upstream electrode 18a and the downstream electrode 18b. Ink droplets are ejected.

  Here, in the case of the ejection electrode 18 having the structure shown in FIG. 3, the upstream electrode 18a of each channel is electrically shared so that a voltage of +300 [V] is always applied at a constant timing. May be. In the case of the electrode shown in FIG. 4, the downstream electrode 18b may be electrically common, and a voltage of +300 [V] may be applied at a constant timing. Thus, by making the upstream electrode 18a or the downstream electrode 18b common to each channel, it is possible to simplify the control unit that controls these electrodes. In this case, the voltage of +300 [V] is applied to the upstream electrode 18a or the downstream electrode 18b even during non-ejection. However, the upstream electrode 18a of the discharge electrode 18 in FIG. 3 has a smaller area than the downstream electrode, and the downstream electrode 18b in FIG. 4 has a smaller area than the upstream electrode 18a as well. An electric field sufficient to eject ink from the electrodes cannot be formed. Therefore, no ink is ejected from the ejection port 28.

  In the discharge electrode having the structure shown in FIG. 1B, FIG. 3 and FIG. 4, it is sufficient that a voltage is applied to each electrode constituting the discharge electrode 18 at the same voltage value at least at the start of discharge. After the discharge is started, the application time (pulse width) of the voltage applied to each electrode may be different. The pulse width of the voltage applied to each electrode may be different for each channel. For example, in the case of the ejection electrode 18 having the shape shown in FIG. 3, the pulse width of the drive voltage applied to the upstream electrode 18a when forming one pixel or one dot may be different for each channel. That is, as shown in FIG. 12, the pulse width of the drive voltage applied to the upstream electrode 18a of the first channel is controlled to be different from the pulse width of the drive voltage applied to the upstream electrode 18a of the second channel. May be. Thus, by changing the pulse width of the drive voltage applied to the upstream electrode 18a for ink ejection for each channel, the appropriate amount of liquid ejected toward the recording medium can be changed for each channel, and the recording can be performed. The gradation of the image formed on the medium can be controlled. At this time, a voltage having the same pulse width can be applied to all the downstream electrodes 18b of the respective channels. Moreover, the pulse width may be the same as the pulse width applied to the downstream electrode 18b, or may be different as shown in FIG. In this case, voltage application to the downstream electrode 18b of each channel can be controlled in common, and the configuration of the control unit can be simplified.

  As described above, the method for controlling the voltage applied to the divided discharge electrodes has been described using the timing chart. However, the voltage values applied to the respective electrodes constituting the discharge electrode are merely examples, and the respective electrodes constituting the discharge electrode. The voltage value can be changed according to the shape of the nozzle, the shape of the discharge port, the ink used, and the like.

  Next, in the case of using the ink jet head 10 shown in FIGS. 1A and 1B, that is, in the case of using the ink jet head in which the discharge electrode is divided into four, the discharge action of the ink droplet R is taken as an example. Will be described in detail.

As shown in FIG. 1A, in the inkjet head 10, a color charged to the same polarity as the voltage applied to the ejection electrode 18 at the time of recording, for example, positive (+) by an ink circulation mechanism including a pump (not shown). Ink Q containing material particles circulates in the ink flow path 30 in the direction of the arrow (from the left to the right in the figure).
On the other hand, at the time of recording, the recording medium P is supplied to the counter electrode 24 and is charged by the charging unit 26 to a polarity opposite to that of the color material particles, that is, negative high voltage (for example, −1500 [V]). In a charged state, it is electrostatically attracted to the counter electrode 24.
In this state, the recording medium P (counter electrode 24) and the inkjet head 10 are moved relative to each other, and each of the electrodes constituting the ejection electrode 18 by the control unit 33 according to the supplied image data is described above. Control is performed so that a pulse voltage having the same voltage value (hereinafter referred to as a drive voltage) is applied at such an application timing. Basically, the ink droplet R is modulated and ejected according to the image data by ejecting on / off by applying the drive voltage on / off, and an image is recorded on the recording medium P.

Here, in a state where the drive voltage is not applied to the ejection electrode 18 (or in a state where the applied voltage is at a low voltage level), that is, in a state where a bias voltage is applied to the counter electrode 24, the ink Q Coulomb attractive force acting between the counter electrode 24 and the color material particles (charged particles) of the ink Q, Coulomb repulsive force between the color material particles, viscosity of the carrier liquid, surface tension, dielectric polarization force, and the like are acting. These are coupled to move the color material particles and the carrier liquid. As shown conceptually in FIG. 1A, the ink Q has a meniscus shape slightly raised from the ejection port 28 and is balanced. It is taken.
Further, the color material particles are aggregated in the discharge port 28 by an electric field generated from at least one of the upstream electrode 18 a and the downstream electrode 18 b constituting the discharge electrode 18. The colorant particles at the ejection port 28 move toward the recording medium P charged by the counter electrode 24 by so-called electrophoresis due to the above-described Coulomb attractive force or the like. Accordingly, the ink Q is concentrated in the meniscus formed at the ejection port 28.

  From this state, a drive voltage, that is, a voltage having the same voltage value is applied to each electrode constituting the ejection electrode 18. As a result, the drive voltage is superimposed on the bias voltage, and the motion coupled by the superposition of the drive voltage further occurs in the previous coupling. An electrostatic force acts on the colorant particles and the carrier liquid by an electric field generated by applying a drive voltage to the ejection electrode 18. The electrostatic force causes the colorant particles and the carrier liquid to be pulled to the bias voltage (counter electrode) side, that is, the recording medium P side, so that the meniscus formed at the ejection port grows upward and substantially above the ejection port 28. A conical ink liquid column so-called tailor cone is formed. Similarly to the above, the color material particles are moved to the meniscus by electrophoresis and the electric field from the upstream electrode or the downstream electrode, and the meniscus ink Q is concentrated and has a large number of color material particles. Almost uniform high density state.

After a finite time has elapsed after the start of application of the drive voltage to each electrode constituting the discharge electrode 18, the color material particles and the carrier mainly at the tip portion of the meniscus having a high electric field strength due to movement of the color material particles or the like. The balance with the surface tension of the liquid is lost, and the meniscus grows abruptly to form elongated ink liquid columns having a diameter of about several μm to several tens of μm, which are called kite strings.
Further, when a finite time elapses, the silk thread grows, and the growth of the silk thread, vibration caused by Rayleigh / Weber instability, uneven distribution of colorant particles in the meniscus, uneven distribution of electrostatic field on the meniscus, etc. The silk thread is broken by the interaction. Then, the divided string is ejected as ink droplets R, flies toward the recording medium, and is pulled by the bias voltage to land on the recording medium P. It should be noted that the growth and splitting of the kite and the movement of the color material particles to the meniscus (spinner) occur continuously during the application of the drive voltage. Therefore, the ejection amount of ink droplets per pixel or per dot can be adjusted by adjusting the time for applying the drive voltage.
Further, when the application of the driving voltage is finished (discharge is turned off), the state returns to the state of the meniscus to which only the bias voltage is applied.

Here, in the inkjet head 10 shown in FIGS. 1A and 1B, each electrode constituting the ejection electrode 18 is exposed to the ink flow path 30. That is, each electrode is in contact with the ink Q in the ink flow path 30.
As described above, when the drive voltage is applied to the discharge electrode 18 in contact with the ink Q in the ink flow path 30 (discharge is turned on), a part of the charge supplied to the discharge electrode 18 is injected into the ink Q, and the discharge port 28. The conductivity of the ink Q located between the discharge electrode 18 and the discharge electrode 18 is increased. In the present invention, the voltage having the same polarity as that of the color material particles can be applied to the downstream electrode 18b at the time of non-ejection, that is, when the driving voltage is not applied. Injected, the conductivity of the ink can be further increased. Further, by applying a voltage having a polarity opposite to that of the color material particles to the upstream electrode 18a, the color material particles floating in the ink are quickly guided to the ejection port, and such color material particles and The charged color material particles floating in the flowing ink are pressed against the ejection port 28 by the electrostatic force generated by the downstream electrode 18b. Therefore, in the inkjet head 10 of the present invention, the ink Q is in a state in which it is easy to eject the ink droplet R when the drive voltage is applied to the ejection electrode 18 (when ejection is on) (ejection performance is improved). ).

  As described above, in the ink jet head of the present invention, the divided discharge electrodes are formed at the discharge ports, and a predetermined voltage is applied to the divided discharge electrodes at the time of non-discharge, so that the color to the discharge ports 28 is increased. Improves the supply of material particles. Therefore, even if large dots are continuously formed, the color material particles are supplied promptly and an image can be stably formed on the recording medium. Further, since the color material particles can be aggregated at the ejection port, the density of the ink ejected from the ejection port is high, and a high-quality image can be formed on the recording medium. In addition, since the ejection port from which ink is ejected is a long hole in the ink flow direction, clogging is unlikely to occur and ink droplets having a desired shape can be ejected from the ejection port stably over a long period of time.

Here, the ink used for the inkjet head 10 of this invention is demonstrated.
Ink Q is obtained by dispersing colorant particles in a carrier liquid. The carrier liquid is preferably a dielectric liquid (nonaqueous solvent) having a high electric resistivity (10 ⁹ Ω · cm or more, preferably 10 ¹⁰ Ω · cm or more). If the electric resistance of the carrier liquid is low, the carrier liquid itself is charged by charge injection due to the drive voltage applied to the control electrode, and the colorant particles do not concentrate. In addition, a carrier liquid having a low electrical resistance is not suitable because there is a concern of causing electrical conduction between adjacent control electrodes.

The relative dielectric constant of the dielectric liquid used as the carrier liquid is preferably 5 or less, more preferably 4 or less, and still more preferably 3.5 or less. By setting the relative dielectric constant in such a range, an electric field effectively acts on the colorant particles in the carrier liquid, and migration easily occurs.
Note that the upper limit value of the specific electric resistance of such a carrier liquid is desirably about 10 ¹⁶ Ω · cm, and the lower limit value of the relative dielectric constant is desirably about 1.9. The reason why it is desirable that the electric resistance of the carrier liquid is in the above range is that if the electric resistance is low, ink ejection under a low electric field is deteriorated, and the reason why the relative dielectric constant is preferably in the above range is the reason. This is because, when the dielectric constant increases, the electric field is relaxed by the polarization of the solvent, and the color of the dots formed thereby becomes thin or causes blurring.

  The dielectric liquid used as the carrier liquid is preferably a linear or branched aliphatic hydrocarbon, alicyclic hydrocarbon, or aromatic hydrocarbon, and halogen-substituted products of these hydrocarbons. For example, hexane, heptane, octane, isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, cyclohexane, cyclooctane, cyclodecane, benzene, toluene, xylene, mesitylene, Isopar C, Isopar E, Isopar G, Isopar H, Isopar L, Isopar M (isopar: trade name of Exxon), Shellsol 70, Shellsol 71 (shellsol: trade name of Shell Oil), Amsco OMS, Amsco 460 Solvent (trade name of Amsco: Spirits), Silicone oil (for example, KF-96L manufactured by Shin-Etsu Silicone) or the like can be used alone or in combination.

  The colorant particles dispersed in such a carrier liquid may be dispersed in the carrier liquid as the colorant itself as colorant particles, but preferably contain dispersed resin particles for improving fixability. When the dispersed resin particles are included, the pigment is generally coated with the resin material of the dispersed resin particles to form resin-coated particles, and the dye is colored with the dispersed resin particles to form colored particles. Is common.

As the coloring material, any of conventional pigments and dyes used in a flow channel kujet ink composition, a printing (oil-based) ink composition, or an electrophotographic liquid developer can be used.
As the pigment used as the color material, regardless of inorganic pigments or organic pigments, those generally used in the technical field of printing can be used. Specifically, for example, carbon black, cadmium red, molybdenum red, chrome yellow, cadmium yellow, titanium yellow, chromium oxide, viridian, cobalt green, ultramarine blue, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment Conventionally known pigments such as quinacridone pigments, isoindolinone pigments, dioxazine pigments, selenium pigments, perylene pigments, perinone pigments, thioindigo pigments, quinophthalone pigments and metal complex pigments are used without particular limitation. be able to.
As dyes used as coloring materials, azo dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinoneimine dyes, xanthene dyes, aniline dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes And oil-soluble dyes such as phthalocyanine dyes and metal phthalocyanine dyes.

Further, as dispersed resin particles, for example, rosins, rosin-modified phenol resins, alkyd resins, (meth) acrylic polymers, polyurethane, polyester, polyamide, polyethylene, polybutadiene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl alcohol, acetal-modified Products, polycarbonate and the like.
Among these, from the viewpoint of ease of particle formation, the weight average molecular weight is in the range of 2,000 to 1,000,000 and the polydispersity (weight average molecular weight / number average molecular weight) is 1.0 to 5 Polymers in the range of 0.0 are preferred. Furthermore, from the viewpoint of ease of fixing, a polymer having any one of a softening point, a glass transition point, and a melting point within a range of 40 ° C. to 120 ° C. is preferable.

  In the ink Q, the content of the color material particles (the total content of the color material particles or further dispersed resin particles) is preferably contained in the range of 0.5 to 30% by weight with respect to the whole ink, and more preferably. Is preferably contained in the range of 1.5 to 25% by weight, more preferably 3 to 20% by weight. If the content of the colorant particles is reduced, problems such as insufficient printed image density or difficulty in obtaining a strong image due to difficulty in obtaining the affinity between the ink Q and the surface of the recording medium P are likely to occur. On the other hand, when the content increases, it becomes difficult to obtain a uniform dispersion, or the ink Q is easily clogged with an inkjet head or the like, and it is difficult to obtain stable ink discharge. .

  The average particle diameter of the colorant particles dispersed in the carrier liquid is preferably 0.1 to 5 μm, more preferably 0.2 to 1.5 μm, and still more preferably 0.4 to 1.0 μm. . This particle size is determined by CAPA-500 (trade name, manufactured by Horiba, Ltd.).

After the colorant particles are dispersed in the carrier liquid (a dispersant may be used if necessary), the chargeant is added to the carrier liquid to charge the colorant particles, and the charged colorant The ink Q is obtained by dispersing particles in a carrier liquid. When dispersing the colorant particles, a dispersion medium may be added as necessary.
As an example of the charge control agent, various materials used in electrophotographic liquid developers can be used. Also, “Recent development and commercialization of electrophotographic development systems and toner materials”, pages 139 to 148, “The Basics and Applications of Electrophotographic Technology” edited by Electrophotographic Society, pages 497 to 505 (Corona Inc., published in 1988), Yuji Harasaki Various charge control agents described in “Electrophotography” 16 (No. 2), p. 44 (1977) can also be used.

The color material particles may be positively charged or negatively charged as long as they have the same polarity as the drive voltage applied to the control electrode.
The charge amount of the color material particles is preferably in the range of 5 to 200 μC / g, more preferably 10 to 150 μC / g, and still more preferably 15 to 100 μC / g.

In addition, since the electric resistance of the dielectric solvent may change due to the addition of the charge control agent, the distribution ratio P defined below is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more. And
P = 100 × (σ1−σ2) / σ1
Here, σ1 is the electrical conductivity of the ink Q, and σ2 is the electrical conductivity of the supernatant obtained by applying the ink Q to the centrifuge. The electrical conductivity was measured using an LCR meter (AG-4311 manufactured by Ando Electric Co., Ltd.) and an electrode for liquid (LP-05 type manufactured by Kawaguchi Electric Manufacturing Co., Ltd.), applied voltage 5 [V], frequency 1 kHz. It is the value which measured on condition of this. Centrifugation was performed for 30 minutes using a small high-speed cooling centrifuge (Tomy Seiko Co., Ltd. SRX-201) under conditions of a rotational speed of 14500 rpm and a temperature of 23 ° C.
By using the ink Q as described above, migration of charged particles is likely to occur, and concentration is facilitated.

The electrical conductivity of the ink Q is preferably 100 to 3000 pS / cm, more preferably 150 to 2500 pS / cm, and still more preferably 200 to 2000 pS / cm. By setting the electric conductivity in the above range, the voltage applied to the control electrode does not become extremely high, and there is no fear of causing electrical continuity between adjacent recording electrodes.
The surface tension of the ink Q is preferably in the range of 15 to 50 mN / m, more preferably 15.5 to 45 mN / m, and still more preferably 16 to 40 mN / m. By setting the surface tension within this range, the voltage applied to the control electrode does not become extremely high, and the ink does not leak around the head to be contaminated.
Furthermore, the viscosity of the ink Q is preferably 0.5 to 5 mPa · sec, more preferably 0.6 to 3.0 mPa · sec, and still more preferably 0.7 to 2.0 mPa · sec.

As an example, such an ink Q can be prepared by dispersing color material particles in a carrier liquid to form particles, and adding a charge adjusting agent to the dispersion medium to cause the color material particles to be charged. Specific methods include the following methods.
(1) A method in which a color material or further dispersed resin particles are mixed (kneaded) in advance, and then dispersed in a carrier liquid using a dispersant as required, and a charge adjusting agent is added.
(2) A method in which a coloring material, or further dispersed resin particles and a dispersing agent are simultaneously added to a carrier liquid, dispersed, and a charge adjusting agent is added.
(3) A method in which a coloring material and a charge adjusting agent, or further dispersed resin particles and a dispersing agent are simultaneously added to a carrier liquid and dispersed.

FIG. 13 shows a conceptual diagram of an embodiment of the ink jet recording apparatus of the present invention, which uses the ink jet head for carrying out the ink jet head control method of the present invention.
An ink jet recording apparatus 60 (hereinafter referred to as a printer 60) shown in the figure is an apparatus that performs four-color printing on one side of a recording medium P, and includes a conveying means for the recording medium P, an image recording means, and a solvent recovery means. Yes, these are housed in a housing 61.
The conveying means includes a feed roller pair 62, a guide 64, rollers 66 (66a, 66b and 66c), a conveying belt 68, a conveying belt position detecting means 69, an electrostatic adsorption means 70, a static eliminating means 72, a peeling means 74, and a fixing. -It has the conveyance means 76 and the guide 78. The image recording forming unit includes a head unit 80, an ink circulation system 82, a head driver 84, and a recording medium position detecting unit 86. Further, the solvent recovery means includes a discharge fan 90 and a solvent recovery device 92.

  In the conveyance means for the recording medium P, the feed roller pair 62 is a conveyance roller pair provided adjacent to the carry-in port 61 a provided on the side surface of the housing 61. The feed roller 62 feeds the recording medium P supplied from a stocker (not shown) to the transport belt 68 (portion supported by the roller 66a). The guide 64 is provided between the feed roller pair 62 and a roller 66 a that supports the conveyance belt 68, and guides the recording medium P to the conveyance belt 68.

It should be noted that a foreign matter removing means for removing foreign matter such as dust and paper dust adhering to the recording medium P is preferably provided in the vicinity of the feed roller pair 62.
As the foreign matter removing means, one or more of non-contact methods such as known suction removal, blow-off removal, electrostatic removal, and contact methods using brushes, rollers, etc. may be used in combination. Alternatively, the feed roller pair 62 may be a slightly adhesive roller, and a cleaner for the feed roller pair 62 may be provided to remove foreign matters such as dust and paper powder when the recording medium P is fed by the feed roller pair 62.

The conveyor belt 68 is an endless belt stretched around the three rollers 66. At least one of the rollers 66a, 66b, and 66c is connected to a drive source (not shown), and rotates the conveyor belt 68.
The conveyance belt 68 functions as a platen for holding the recording medium P in addition to the scanning conveyance means for the recording medium P during image recording by the head unit 80, and further conveys the image to the fixing / conveyance means 76 after image recording. Therefore, the transport belt 68 is preferably formed of a material having excellent dimensional stability and durability. For example, the transport belt 68 is formed of a metal, a polyimide resin, a fluororesin, another resin, or a composite thereof.

In the illustrated example, since the recording medium P is held on the conveyance belt 68 by electrostatic attraction, the conveyance belt 68 is insulative on the side (front surface) that holds the recording medium P and is in contact with the roller 66 (back surface). ) Has conductivity. In the illustrated example, the roller 66a is a conductive roller, and the back surface of the transport belt 68 is grounded via the roller 66a.
That is, the conveyance belt 68 functions as the counter electrode 24 composed of the electrode substrate 24a and the insulating sheet 24b shown in FIG. 1A when holding the recording medium P.

As such a conveyor belt 68, a resin sheet and a metal belt are bonded to each other with a belt coated with any of the above resin materials, an adhesive, etc. For example, a belt having a metal layer and an insulator may be used, such as a metal belt or a belt formed by metal vapor deposition on the back surface of the belt made of the resin.
Further, it is preferable that the surface of the conveying belt 68 that contacts the recording medium P is smooth, and thereby, good adsorbability of the recording medium P can be obtained.

  The conveyor belt 68 is preferably suppressed from meandering by a known method. As a meandering suppression method, for example, the roller 66c is a tension roller, and the shaft of the roller 66c is adjusted between the roller 66a and the roller 66b in accordance with the output of the conveying belt position detecting means 69, that is, the detecting position in the width direction of the conveying belt 68. A method of suppressing meandering by changing the tension at both ends in the width direction of the conveyor belt by tilting with respect to the axis is exemplified. Further, the meandering may be suppressed by forming the roller 66 in a tapered shape, a crown shape, or other shapes.

  Here, as described above, the conveying belt position detecting unit 69 suppresses the meandering of the conveying belt and regulates the position of the recording medium P in the scanning conveying direction at the time of image recording to a predetermined position. 68 is used to detect the position in the width direction, and known detection means such as a photosensor is used.

The electrostatic attraction means 70 applies a predetermined bias voltage to the head unit 80 (the ink jet head of the present invention) to the recording medium P and attracts it to the conveying belt 68 by electrostatic force to hold it. Is charged to a predetermined potential.
In the illustrated example, the electrostatic attraction unit 70 includes a scorotron charger 70a for charging the recording medium P, and a negative high-voltage power supply 70b connected to the scorotron charger 70a. While the recording medium P is conveyed by the feed roller pair 62 and the conveying belt 68, the recording medium P is charged with a negative bias voltage by the scorotron charger 70a connected to the negative high voltage power source 70b, and is applied to the insulating layer of the conveying belt 68. It is electrostatically attracted.

In addition, the conveyance speed of the conveyance belt 68 when charging the recording medium P may be in a range that can be stably charged, and may be the same as or different from the conveyance speed at the time of image recording. Alternatively, the recording medium P may be rotated a plurality of times so that the electrostatic adsorption means acts on the same recording medium P a plurality of times to perform uniform charging.
In the illustrated example, the electrostatic adsorption unit 70 performs electrostatic adsorption and charging of the recording medium P. However, the electrostatic adsorption unit and the charging unit may be provided separately.

  The electrostatic attraction means is not limited to the illustrated scorotron charger 70a, and various other means and methods such as a corotron charger, a solid charger, and a discharge needle can be used. Further, as will be described in detail later, at least one of the rollers 66 is a conductive roller, or a conductive platen is provided on the back surface side (opposite side of the recording medium P) of the conveying belt 68 at the recording position on the recording medium P. By arranging and connecting this conductive roller or conductive platen to a negative high voltage power source, the electrostatic attraction means 70 may be configured, or the conveying belt 68 is an insulating belt and the conductive roller is grounded. The conductive platen may be connected to a negative high voltage power source.

The recording medium P charged by the electrostatic attraction means 70 is transported to the position of the head unit 80 described later by the transport belt 68.
The head unit 80 records an image on the recording medium P by ejecting ink droplets according to image data using an inkjet head that performs the inkjet head control method of the present invention. Here, the ink jet head of the present invention discharges the ink droplet R by superimposing the drive voltage on the bias voltage by applying the drive voltage to the discharge electrode 18 with the charging potential of the recording medium P as the bias voltage, The image is recorded on the recording medium P as described above. At this time, by providing a heating means for the conveying belt 68 and increasing the temperature of the recording medium P, fixing of the ink droplets R on the recording medium P can be promoted, and bleeding is further suppressed and image quality is improved. Can be achieved.
The image recording by the head unit 80 or the like will be described in detail later.

The recording medium P on which the image is recorded is discharged by the discharging unit 72, peeled off from the transport belt 68 by the peeling unit 74, and transported to the fixing / transporting unit 76.
In the illustrated example, the static elimination unit 72 is a so-called AC corotron static eliminator having a corotron static eliminator 72a, an AC power source 72b, and a DC high-voltage power source 72c grounded at one end. In addition to the above, as the static elimination means, various means and methods such as a scorotron static eliminator, a solid charger, a discharge needle, etc. can be used, and a conductive roller, A configuration using a conductive platen is also preferably used.
As the peeling means 74, a known technique such as a peeling blade, a reverse rotation roller, an air knife or the like can be used.

The recording medium P peeled off from the conveying belt 68 is sent to the fixing / conveying means 76, and the image formed by ink jet is fixed. A roller pair including a heat roller 76a and a conveyance roller 76b is used as the fixing / conveying means 76, and the recorded image is heated and fixed while the recording medium P is nipped and conveyed.
The recording medium P on which the image is fixed is guided by a guide 78 and discharged to a discharge stocker (not shown).

Examples of the heat fixing means include general heat fixing such as irradiation with infrared rays or a halogen lamp or a xenon flash lamp, or hot air fixing using a heater, in addition to the heat roll fixing described above. In the heat fixing / conveying means 76, the heating means performs only heating, and the conveying means and the heat fixing means may be provided separately.
In the case of heat fixing, when coated paper or laminated paper is used as the recording medium P, a phenomenon called blistering occurs in which the water inside the paper rapidly evaporates due to a rapid temperature rise and the paper surface is uneven. May occur. In order to prevent this, it is preferable to arrange a plurality of fixing devices and change one or both of the power supply of each fixing device and the distance to the recording medium P so that the temperature of the recording medium P gradually increases.

The printer 60 is preferably configured so that nothing touches the image recording surface of the recording medium P from at least the image recording by the head unit 80 until the fixing by the fixing / conveying means 76 is completed.
Further, the moving speed of the recording medium P at the time of fixing in the fixing / conveying means 76 is not particularly limited, and may be the same as or different from the conveying speed by the conveying belt 68 at the time of image formation. . When the conveyance speed is different from that at the time of image formation, it is preferable to provide a speed buffer for the recording medium P immediately before the fixing / conveyance means 76.

Hereinafter, image recording in the printer 60 will be described in detail.
As described above, the image recording means of the printer 60 includes the head unit 80 that discharges the ink jet, the ink circulation system 82 that supplies and recovers the ink Q to the head unit 80, a computer (not shown), a RIP (Raster Image Processor), and the like. A head driver 84 that drives the head unit 80 by an output image signal from an external device, and a recording medium position detecting unit 86 that detects the recording medium P in order to determine the image recording position in the recording medium P are configured.

FIG. 13B is a perspective view schematically showing the head unit 80 and the conveying means for the recording medium P around it.
The head unit 80 has four inkjet heads 80a corresponding to ink ejection of four colors of cyan (C), magenta (M), yellow (Y), and black (K) for recording a full color image. Then, in accordance with a signal from the head driver 84 supplied with the image data, the ink Q supplied by the ink circulation system 82 is ejected as an ink droplet R, and the recording medium P being conveyed by the conveying belt 68 at a predetermined speed. Record an image on The inkjet heads 80 a for the respective colors are arranged in the conveyance direction of the conveyance belt 68.
In addition, the inkjet head 80a of each color of the head unit 80 is an inkjet head according to the present invention.

In the illustrated example, the inkjet heads 80a are line heads in which the ejection ports 28 are arranged in the entire width direction of the recording medium P, and are preferably arranged in a staggered manner as shown in FIG. And a multi-channel head having a plurality of nozzle rows.
Accordingly, in the illustrated example, the recording medium P is held by the transport belt 68 and the recording medium P is simply passed through the head unit 80 once by transport, that is, only one scanning transport is performed. An image is formed on the entire surface of the recording medium P. Therefore, image recording (drawing) can be performed at a higher speed than when the ejection head is serially scanned.

The ink jet head of the present invention can also be used for a so-called serial head (shuttle type). Therefore, the printer 60 may also be in this mode.
In this case, the head unit 80 is configured by aligning the row of the ejection ports 28 of each inkjet head (which may be single row or multi-channel) with the carrying direction of the carrying belt 68, and the head unit 80 is carried by the recording medium P. Scanning means for scanning in a direction orthogonal to the direction is provided. As the scanning means, known scanning means can be used.
The image recording may be performed in the same manner as a normal shuttle type ink jet printer. The recording medium P is intermittently conveyed by the conveying belt 68 according to the length of the row of the ejection ports 28, and is synchronized with the intermittent conveyance. Then, at the time of stop, the head unit 80 is scanned to record an image on the entire surface of the recording medium P.
Thus, the image formed on the entire surface of the recording medium P by the head unit 80 is fixed by the fixing / conveying means 76 by the recording medium P being nipped and conveyed by the fixing / conveying means 76 as described above. Is done.

The head driver 84 receives image data from an external device, receives image data from a system control unit (not shown) that performs various processes, and drives the head unit 80 based on the image data.
This system control unit performs color separation, division into appropriate numbers of pixels and gradations, etc. on image data received from external devices such as computers, RIPs, image scanners, magnetic disk devices, and thumbtack data transmission devices. This is a part that is used as image data for the head driver 84 to drive the head unit 80 (inkjet head). Further, the system control unit controls the ink ejection timing by the head unit 80 in accordance with the conveyance timing of the recording medium P by the conveyance belt 68. The discharge timing is controlled by using an output from the recording medium position detecting unit 86 and an output signal from the encoder disposed on the conveying belt 68 or the driving unit of the conveying belt 68.
The recording medium position detection means 86 is for detecting the recording medium P conveyed to the ink droplet ejection position by the head unit 80, and an already known detection means such as a photosensor is used. it can.
Here, the head driver 84 divides the drawing when there are a large number of ejection units (number of channels) to be controlled, such as when a line head is applied, and a known resistance matrix driving method or resistance diode matrix driving method. May be used. Thereby, the number of ICs used by the head driver 84 can be reduced, and the cost can be reduced and the control circuit size can be suppressed.

  The ink circulation system 82 is for flowing the ink Q through the ink flow path 30 (see FIG. 2) of the ink jet head 80a of each color of the head unit 80, and ink of each of four colors (C, M, Y, K). An ink circulation device 82a having a tank, a pump, a replenishment ink tank (not shown), and the like, and ink Q of each color is supplied from the ink tank of the ink circulation device 82a to the ink flow path 30 of each color inkjet head of the head unit 80 An ink supply system 82b for recovering ink from the ink flow path 30 of the ink jet head of each color of the head unit 80 to the ink circulation device 82a.

The ink circulation system 82 supplies ink Q for each color from the ink tank to the head unit 80 via the ink supply system 80b by the ink circulation device 82a, and for each color from the head unit 80 via the ink supply system 80c. Any ink Q can be used as long as it can be collected and circulated in the ink tank.
The ink tank stores ink Q of each color, and the ink Q is pumped out by a pump and sent to the head unit 80. As the ink is discharged from the head unit 80, the density of the ink circulating in the ink circulation system 82 is decreased. In the ink circulation system 82, the ink density is detected by the ink density detector and replenished accordingly. It is desirable to appropriately replenish ink from the ink tank and maintain the ink density within a predetermined range.

Further, the ink tank is preferably provided with a stirring device for suppressing precipitation / concentration of the solid component of the ink and an ink temperature management device for suppressing temperature change of the ink. This is because if the temperature is not controlled, the ink temperature changes due to changes in the environmental temperature, etc., and the dot diameter changes due to changes in the physical properties of the ink, making it impossible to stably form high-quality images. Because there is.
As the stirring device, a rotary blade, an ultrasonic vibrator, a circulation pump, or the like can be used.
As the ink temperature control device, a known method such as a method in which a heating element such as a heater or a Peltier element or a cooling element is provided in the head unit 80, ink tank, ink distribution pipe system, etc., and control is performed by a temperature sensor, for example, a thermostat. Can be used. When the temperature control device is arranged in the ink tank, it is preferable to arrange it together with the stirring device so as to make the temperature distribution constant. Further, the stirring device for keeping the concentration distribution in the tank constant may be shared with the stirring device for suppressing the precipitation and concentration of the solid component of the ink.

As described above, the printer 60 has the solvent recovery means including the exhaust fan 90 and the solvent recovery device 92. The solvent recovery means recovers the carrier liquid that evaporates from the ink droplets ejected from the head unit 80 onto the recording medium P, particularly the carrier liquid that evaporates from the recording medium P when fixing the image formed by the ink droplets. To do.
The discharge fan 90 is for sucking air inside the casing 61 of the printer 60 and sending it to the solvent recovery device 92.
The solvent recovery device 92 includes a solvent vapor absorber, and adsorbs the solvent component of the gas containing the solvent vapor sucked by the exhaust fan 90 to the solvent vapor absorber, and the gas after the solvent is adsorbed and recovered. The paper is discharged out of the casing 61 of the printer 60. As the solvent vapor absorbing material, various activated carbons are preferably used.

  In the above description, an electrostatic ink jet recording apparatus that records a color image using four color inks of C, M, Y, and K has been described. However, the present invention is not limited to this, and a monochrome recording apparatus Alternatively, recording may be performed using an arbitrary number of inks of other colors, for example, light colors or special colors. In that case, the number of head units 80 and ink circulation systems 82 corresponding to the number of ink colors are used.

  In each of the above examples, the ink jet discharges ink droplets R by charging the color material particles in the ink positively and setting the opposite electrode on the back of the recording medium or recording medium P to a negative high voltage. However, the present invention is not limited to this, and conversely, the color material particles in the ink may be negatively charged, and the recording medium or the counter electrode may be set to a positive high voltage to perform image recording by inkjet. . Thus, when the polarity of the colored charged particles is reversed from the above example, the polarity of the voltage applied to the electrostatic adsorption means, the counter electrode, and the drive electrode of the inkjet head may be reversed from the above example. .

  The inkjet head, the inkjet head control method, and the inkjet recording apparatus according to the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiment, and various improvements can be made without departing from the gist of the present invention. Of course, you may make changes.

(A) is a cross-sectional view schematically showing an ink jet head according to the present invention, and (B) is a view schematically showing a planar configuration of an ejection electrode. It is the figure which showed typically a mode that the several discharge outlet was arranged in two-dimensionally on the discharge outlet board | substrate of an inkjet head. This is a configuration example different from FIG. 1B of the ejection electrode of the inkjet head of the present invention. FIG. 1B shows another configuration example of the ejection electrode of the inkjet head of the present invention. It is the figure which showed typically the planar structure of the guard electrode of the inkjet head of a multichannel structure. 3 is a timing chart of voltages applied to each electrode of the ejection electrode shown in FIGS. FIG. 7 is a timing chart different from FIG. 6 showing the voltage applied to each electrode of the ejection electrodes shown in FIGS. It is a timing chart when the voltage applied to the upstream electrode and the downstream electrode is always applied at a constant timing regardless of the image data during ejection. It is an example of the timing chart of the voltage applied to the discharge electrode which has the shape shown in FIG. It is an example of the timing chart of the applied voltage different from FIG. 9 of the timing chart of the voltage applied to the discharge electrode which has the shape shown in FIG. FIG. 10 is an example of a timing chart of an applied voltage which is different from FIG. 9 of the timing chart of the voltage applied to the ejection electrode having the shape shown in FIG. 3. FIG. 4 is an example of a timing chart when the pulse width of the drive voltage applied to the upstream electrode of the ejection electrode having the shape shown in FIG. 3 is varied for each channel. It is a conceptual diagram of an example of an inkjet recording device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Inkjet head 12 Head substrate 14 Ink guide 14a Tip part 16 Discharge port substrate 18 Discharge electrode 18a Upstream electrode 18b Upstream electrode 18c, 18d Intermediate electrode 20 Guard electrode 24 Counter electrode 24a Electrode substrate 24b Insulating sheet 26a Scorotron charger 26b Bias Voltage source 28 Each ejection port 30 Ink flow path 32 Insulating substrate 33 Control unit 34 Insulating layer 36 Opening 60 Inkjet recording apparatus (inkjet printer)
62 Feed roller 64 Guide 66 Roller 66a Roller 68 Conveying belt 69 Conveying belt position detecting means 70 Electrostatic adsorption means 70a Scorotron charger 70b High voltage power supply 72 Discharge means 72a Corotron neutralizer 72b AC power supply 72c DC high voltage power supply 76 Fixing / conveying means 76a Heat roller 78 Guide 80 Head unit 80a Each inkjet head 80b, 80c Ink supply system 82 Ink circulation system 82a Ink circulation device 82b Ink supply system 82c Ink collection system 84 Head driver 86 Recording medium position detection means 90 Discharge fan P Recording medium Q Ink R Ink droplet

Claims (16)

An electrostatic inkjet head that records an image on a recording medium by discharging an ink containing charged fine particles using an electrostatic force,
An ejection port substrate on which ejection ports for ejecting the ink are formed;
An ink channel provided on the opposite side of the ejection port substrate to the side from which the ink is ejected, and for supplying the ink to the ejection port;
A plurality of electrodes, the plurality of electrodes formed on the discharge port substrate so as to surround the discharge ports, and a discharge electrode to which a voltage for discharging the ink from the discharge ports is applied;
An electrostatic ink jet head having a control unit for controlling voltages applied to the plurality of electrodes constituting the ejection electrode so that an asymmetric electric field is formed at the ejection port when the ink is not ejected. .   2. The control unit according to claim 1, wherein when the ink is ejected, the control unit controls a voltage applied to each of the plurality of electrodes constituting the ejection electrode so that a symmetrical electric field is formed with respect to a center of the ejection port. Electrostatic inkjet head.   The inkjet head according to claim 1, wherein the ejection port is formed in a long hole shape that is long in the ink flow direction of the ink flow path.   The plurality of electrodes constituting the discharge electrode are respectively arranged so as to be asymmetric with respect to a plane perpendicular to the ink flow direction of the ink flow path and including the center of the discharge port. The inkjet head as described in any one of these.   The ejection electrode is disposed upstream of the ejection port in the ink flow direction of the ink flow path and downstream of the upstream electrode, and is substantially C-shaped or substantially co-shaped. The inkjet head according to claim 4, comprising a downstream electrode having a letter shape.   The discharge electrode is disposed downstream of the discharge port in the ink flow direction of the ink flow path and upstream of the downstream electrode, and is substantially C-shaped or substantially co-shaped. The inkjet head according to any one of claims 1 to 3, comprising an upstream electrode having a letter shape.   The plurality of electrodes constituting the ejection electrode are respectively arranged so as to be symmetric with respect to a plane perpendicular to the ink flow direction of the ink flow path and including the center of the ejection port. Inkjet head.   The ejection electrode includes an upstream electrode disposed upstream of the ejection port in the ink flow direction of the ink flow path, a downstream electrode disposed downstream of the ejection port, and the upstream side The inkjet head according to claim 7, wherein the inkjet head is configured by a pair of intermediate electrodes that are located between an electrode and the downstream electrode and are disposed so as to sandwich the discharge port.   The said discharge port is formed in multiple numbers, At least 1 electrode of the some electrode which comprises the said discharge electrode arrange | positioned at each discharge port is mutually electrically common, The any one of Claims 1-8. The inkjet head described in 1.   An inkjet recording apparatus provided with the inkjet head as described in any one of Claims 1-9. An electrostatic inkjet head control method for recording an image on a recording medium by ejecting ink containing charged fine particles using electrostatic force,
The electrostatic ink jet head is provided on a discharge port substrate on which a discharge port for discharging the ink is formed, and on a side opposite to the ink discharge side of the discharge port substrate, and the ink is supplied to the discharge port. An ink flow path for supply and a plurality of electrodes are formed on the discharge port substrate so as to surround the discharge ports, and a voltage for discharging the ink from the discharge ports is applied. And a discharge electrode to be
A control method for controlling a voltage applied to each of the plurality of electrodes constituting the ejection electrode so that an asymmetric electric field is formed with respect to a central axis of the ejection port when the ink is not ejected.   12. The control according to claim 11, wherein a voltage applied to each of the plurality of electrodes constituting the ejection electrode is controlled so that an electric field symmetric with respect to a central axis of the ejection port is formed when the ink is ejected. Method.   The control method according to claim 11 or 12, wherein a voltage having the same voltage value is applied to all the electrodes constituting the ejection electrode when the ink is ejected.   One of the plurality of electrodes constituting the ejection electrode is an upstream electrode disposed on the upstream side in the ink flow direction of the ink flow path, and the charged fine particles are placed on the upstream electrode during non-ejection. The control method as described in any one of Claims 11-13 which applies the voltage of reverse polarity.   One of the plurality of electrodes constituting the ejection electrode is a downstream electrode disposed on the downstream side in the ink flow direction of the ink flow path, and the charged fine particles are placed on the downstream electrode during non-ejection. The control method as described in any one of Claims 11-14 which applies the voltage of the same polarity.   The voltage applied to the plurality of electrodes is controlled so that the application time of the voltage applied to the plurality of electrodes constituting the ejection electrode is different when the ink is ejected. The control method described.

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